1. Field of the Invention
The present invention relates to a light modulating device, and more particularly to a light modulating device capable of producing a color display and a high-resolution monochrome display. The light modulating device of the present invention may be used in a transmission type liquid crystal display device, a reflection type liquid crystal display device, a transmission/reflection type liquid crystal display device, an organic or inorganic EL (electroluminescence) device, an electrophoretic device, and an image reading device.
2. Description of the Background Art
Liquid crystal displays (LCDs) have been used in various applications, primarily in personal applications, for their advantageous features such as a small installation space and a small power consumption. It is expected that LCDs will be used in a wider range of applications and under more various circumstances. An LCD is provided with a color filter for producing a color display. In such a case, each pixel includes three picture elements of the three primary colors of light, i.e., R (red), G (Green) and B (Blue). The combination of the R, G and B picture elements and the ability to produce various gray levels in each picture element make it possible to produce a multi-color display.
It is said that the required resolution is 80 dpi (dots per inch) or more for image information, and 170 dpi or more for photographic images. However, for high-resolution image information such as character information and X-ray images, the required resolution is as high as 200 dpi or more. A color liquid crystal panel, which renders a single color (white or black) by driving three (R, G and B) picture elements, requires a resolution that is three times as high as that of a monochrome liquid crystal panel, which does not require a color filter, in the horizontal direction of the screen.
Therefore, a color liquid crystal panel having a resolution of substantially 600 dpi or more is required for displaying contents with which it is necessary to display a large number of characters clearly, such as novels and newspapers, for example. In order to realize a resolution of 600 dpi or more, individual pixels of a color liquid crystal panel need to be very small. However, it is very difficult to produce a color liquid crystal panel having a resolution of 600 dpi or more with production apparatuses that are commonly used in the art. In addition, as to the driving circuit, it is difficult to set appropriate driving conditions with such a high resolution. With small-size LCDs, it is possible to realize high-resolution LCDs by using techniques such as a time sequential method. With large-size LCDs, however, the substrate is also large, whereby the realization of large-size high-resolution LCDs is hindered by problems such as a delay in the voltage application at locations remote from the signal-input side.
In view of this, liquid crystal display devices have been developed in which the color/monochrome switching is enabled by controlling the color of the liquid crystal panel. For example, Japanese Laid-Open Patent Publication No. 2000-284315 discloses a method for enabling the color/monochrome switching by providing a polymer-dispersed liquid crystal layer between a color filter and a liquid crystal layer, so that light, which has passed through the color filter, passes through the polymer-dispersed liquid crystal layer, where the light is transmitted/scattered. Moreover, Japanese Laid-pen Patent Publication No. 9-244057 discloses another method for enabling the color/monochrome switching by layering an ECB (Electrically Controlled Birefringence) liquid crystal panel on a monochrome liquid crystal panel to utilize the coloring of light based on the birefringence effect of the ECB panel.
However, with the liquid crystal display device disclosed in Japanese Laid-Open Patent Publication No. 2000-284315, the light scattering effect is dependent on the thickness of the polymer-dispersed liquid crystal layer, and the thickness of the polymer-dispersed liquid crystal layer needs to be quite large to obtain a scattering effect that is strong enough to convert RGB light into white light, thereby requiring a very large voltage to be applied.
With the liquid crystal display device disclosed in Japanese Laid-Open Patent Publication No. 9-244057, the color purity is low because a color is produced by using an ECB panel. Moreover, since the transmittance cannot be controlled to an intended value, it is highly likely that an intended hue is not obtained in a color display. Furthermore, since two panels are layered together, a color shift may occur across the displayed image in a color display, and the display may appear in an incongruent manner because of a transmittance shift across a picture element in a monochrome display, due to the parallax between the monochrome liquid crystal panel and the ECB liquid crystal panel.
The present invention has been made in view of these problems in the art, and has an object to provide a light modulating device capable of producing a full-color display and a high-resolution monochrome display.
A light modulating device of the present invention includes: a first substrate on which a first electrode layer and a light amount control layer are deposited in this order; a second substrate on which a second electrode layer and a color filter layer are deposited in this order, the second substrate opposing the first substrate; and a third electrode layer interposed between the light amount control layer and the color filter layer, wherein: a plurality of picture elements are defined in a matrix pattern by the first electrode layer and the third electrode layer; an amount of light transmitted through the light amount control layer is electrically controlled by the first electrode layer and the third electrode layer; and a colored/uncolored state of the color filter layer is electrically controlled by the second electrode layer and the third electrode layer.
It is preferred that the color filter layer is solid or semisolid. The color filter layer may be made of a medium containing an organic electrochromic pigment, or may be a polymer-dispersed liquid crystal layer containing a dichroic pigment.
The color filter layers of the same hue may be arranged in a column direction, and the second electrode layer may be a plurality of stripe-shaped electrode layers, each of which is superposed on the color filter layers of the same hue. The plurality of stripe-shaped electrode layers may be connected to one or more signal lines.
The third electrode layer may be a plurality of picture element electrodes formed in a matrix pattern and each connected to a switching device; and the first electrode layer may be a common electrode layer opposing the plurality of picture element electrodes.
The second electrode layer may be a plurality of color filter electrode layers formed in regions superposed on the plurality of picture element electrodes, respectively; and a signal may be written to each of the plurality of color filter electrode layers via the switching device that is connected to the picture element electrode superposed on the color filter electrode layer. Alternatively, the second electrode layer may be a plurality of color filter electrode layers formed in regions superposed on the plurality of picture element electrodes, respectively; and a signal may be written to each of the plurality of color filter electrode layers via another switching device adjacent to the switching device that is connected to the picture element electrode superposed on the color filter electrode layer.
The plurality of picture element electrodes may be connected to a plurality of source signal lines extending in parallel to one another; and the plurality of color filter electrode layers may be connected to color filter signal lines extending in parallel to one another, the number of the color filter signal lines being equal to the number of the source signal lines.
The first electrode layer may be a plurality of picture element electrodes formed in a matrix pattern and each connected to a switching device; and the third electrode layer may be a common electrode layer opposing the plurality of picture element electrodes.
The light amount control layer may be a liquid crystal layer or an electroluminescence layer.
The term xe2x80x9cpicture elementxe2x80x9d is used herein to refer to the minimum unit whose optical state can be controlled to produce a display. In a color display, typically, the R, G and B minimum display units are referred to as xe2x80x9cR picture elementxe2x80x9d, xe2x80x9cG picture elementxe2x80x9d and xe2x80x9cB picture elementxe2x80x9d, respectively. A set of an R picture element, a G picture element and a B picture element together form a xe2x80x9cpixelxe2x80x9d. In a passive matrix display device, a xe2x80x9cpicture elementxe2x80x9d is defined as a region where one of column electrodes which are arranged in a stripe pattern crosses one of row electrodes which are perpendicular to the column electrodes. In an active matrix display device, a picture element region is defined by a picture element electrode and a common electrode (counter electrode) which opposes the picture element electrode. In an arrangement with a black matrix, strictly speaking, a xe2x80x9cpicture elementxe2x80x9d is a portion of each region across which a voltage is applied according to the intended display state which corresponds to an opening of the black matrix.
A plurality of picture elements are typically arranged in a matrix pattern. Thus, a plurality of picture elements are arranged in the row direction and in the column direction perpendicular to the row direction. Note however that the picture element arrangement is not limited to this, as long as they are arranged in two or more different directions. For example, in a color display device employing a delta arrangement, the column direction may be a slant direction with respect to the row direction. Note that the terms xe2x80x9ccolumn directionxe2x80x9d and xe2x80x9crow directionxe2x80x9d are used herein merely to represent one direction in the display screen and another direction that crosses the first direction, and do not necessarily correspond to the length and width directions in the display screen.